Preloaded ball bearing screw and nut mechanism



Aug. 3, 1965 H. ORNER 3,198,029

PRELOADED BALL BEARING SCREW AND NUT MECHANISM Original Filed July 30,1953 2 Sheets-Sheet 1 F. G a \NVENTOR'.

1965 H. ORNER 3,198,029

PRELOADED BALL BEARING SCREW AND NUT MECHANISM Original Filed July 350,1953 2 Sheets-Sheet 2 E 14 F- 4 i3 4 r i a 11 J 10 T V i g 11' L J 1 It;I

INVENTOR.

HARRY ORN ER United States Patent 3,198,tl2 PRELGADED BALL BEARENG SCREWAND NUT MECHANISM Harry Urner, 2479 Glen Eanyon Read, Aitadena, Caiif.Griginal applications July 39, 1953, Ser. No. 371,253,

and Apr. 2, 1959, Ser. No. 8%,894. Divided and this application Feb. 24,1%1, Ser. No. 91,545

Claims. (El. 74-459) This invention relates to recirculating ballbearing screw and nut mechanisms for changing rotary to linear, orlinear to rotary, motion by means of rolling balls. The invention alsorelates to methods of eliminating end play or backlash, and effectingload dividing, in such mechanisms.

This application is a division of my copending applications Ser. No.371,253, filed July 30, 1953, for Ball Bearing Screw and Nut Mechanism,now abandoned, and Ser. No. 803,804, filed Apr. 2, 1959, for PreloadedBall Bearing Screw and Nut Mechanism, now forfeited, and acontinuation-in-part of Ser. No. 459,605, filed Oct. 1, 1954, forBall-Bearing Screw and Nut Mechanism, now Patent No. 2,895,343.

The ball bearing screw and nut mechanisms as known heretofore consist ofa screw and nut with balls distributed on the spiral race of the nut tocarry a load by the rolling action of the balls. A return tubeconnecting the ends of the race in the nut serves to recirculate theball back to the beginning of the race. This return tube complicates themechanism and limits the functional and economical use of the device andthis is particularly true where the return tube extends outside theconfines of the nut body where it is subject to injury and failure byreason of interference or obstruction to the free circulation of theballs.

An important feature of the invention is the provision made forassembling the principal components with precision and in such mannerthat all balls and the surfaces of the races in contact therewith areloaded uniformly and to values known to a high degree of accuracy. Thesecharacteristics and features have long been sought but never beforeachieved except in a haphazard manner by laborious cut and try assemblyprocedures.

One of the primary objects of this invention is to provide an improvedball bearing screw and nut mechanism eliminating the return tubeconstruction.

Another object of this invention is to provide a ball bearing screw andnut mechanism employing single turn recirculating paths for higherloading and better efliciency.

Another object of this invention is to provide a ball bearing screw andnut mechanism thatv automatically spaces the balls on the spiral race ofthe nut to eliminate the rubbing friction between the balls.

Another object of this invention is to provide a ball bearing screw andnut mechanism of economical construction.

Another object of this invention is to provide a ball bearing screw andnut mechanism incorporating separate and individual circulating systemsassembled into a single articulate nut structure.

Another object of this invention is to provide a ball bearing screw andnut mechanism incorporating individual circulating systems assembledinto a nut in such a way as to control the distribution of the loads onthe balls, and to provide a method of effecting such assembly.

Another object of the invention is to provide a highly simple andeconomical nut means incorporating devices for causing the ball race totake the form of a figure eight.

Another object of the invention is the provision of a ball bearing nutand screw mechanism having a plurality of nut rings each having anindependent closed circuit 3,1983% Patented Aug. 3, 1965 ofrecirculating balls which circuits are of figure eight configuration andinclude a relatively large diameter loop of at least one fullconvolution of balls all in contact with the screw groove, andcharacterized in the provision 5 of means for preloading all balls incontact with the screw to a predetermined value whereby such ballsremain loaded independently of the presence of external loads acting onthe mechanism.

Another object of the invention is the provision of a ball bearing nutand screw mechanism having a plurality of similar nuts each heldassembled to the screw by an independent closed circuit of balls andwherein said nuts are arranged to be rigidly locked against apredetermined position wherein it is known that the balls of eachassociated nut lying in juxtaposition to the screw will be loadeduniformly as an external load is applied to the mechanism.

Other objects and advantages will become more fully apparent asreference is had to the accompanying drawings wherein my invention isillustrated and in which:

FIGURE 1 is a plan view partially in section illustrating a preferredembodiment of the invention during assembly;

FIGURE 2 is an enlarged fragmentary sectional view taken on plane 2-2 ofFIGURE 1;

FIGURE 3 is a plan view, partly in section showing another preferredembodiment of a ball bearing nut and screw mechanism incorporating thepresent invention in a typical operating environment;

FIGURE 4 is a view partly in longitudinal central section taken on line4-4 of FIGURE 3;

FIGURE 5 is a transverse sectional view taken on the broken line 5-5 ofFIGURE 4 and as viewed in the direction of the arrows;

FIGURE 6 is an enlarged fragmentary view taken on line 6-6 on FIGURE 5;

FIGURE 7 is a fragmentary sectional view taken on line 7-7 of FIGURE 6;

FIGURE 8 is a fragmentary sectional view taken on line 8-8 of FIGURE 6;

FIGURE 9 is a detail side elevational view showing the ball returninsert removed from the nut ring;

FIGURES 10 and 11 are end and side elevational views respectively of theball return means; and

FIGURE 12 is a schematic view looking axially of the nut ring butshowing the balls only and in their normal operating figure eightconfiguration.

Referring more particularly to FIGURES 1 and 2 showing one preferredembodiment of the invention and the process of assembly, the ballbearing nut and screw mech anism there shown by way of example includesa screw 1 having its opposite ends mounted in an assembly jig comprisinga pair of L-shaped members 50 having their longer legs extendingparallel and closely beside one lateral edge of screw 1. These legs arerigidly connected together by bolts. Rotatably mounted along theaccurately formed helical groove 16 of screw 1 are a plurality ofidentical nut rings 14 each having in excess of one complete convolutionof an inwardly facing helical groove 15 of the same pitch as groove 16.The nut rings are held assembled to screw 1 by an endless circuit ofidentical balls 18 having a load bearing convolution and a ball returnloop portion located Within the body of the associated nut ring 14 withthe opposite ends of the return loop in communication with the oppositeends of the load grove convolution. The nut rings and the ball returnloops as Well as numerous other constructional details of both the ringsand the associated screw 1- may take various forms, such as thoseillustrated in FIGURES 4 through 12 hereof or in FIGURES 1 to 20 of mycopending application for Letters Patent Serial No. 773,668 filed Nov.13, 1958, now Patent 2,924,113 granted Feb.

. r 3 V Y 9, 1960. Sinceall features of these nut rings, balls and theassociated screw are fully illustrated and described either hereinbelowor in my aforementioned patent, further description will be unnecessary.u 7 V I In assembling the components shown in FIGURES 1 and 2, nutsections A, B, C and D are run ontoscrew 1 and are free to rotaterelative'to one another on balls 18 comprising each continuous ballcircuits of the individual nut sections. e

The opposite ends of screw 1 are then supported in bearings of asuitable rigid framework 50. These supporting bearings for the screw maycomprise the machine in which the mechanism is to be used or an assemblyfixture or tool. Aswill be appreciated, it is immaterial whether thebearing supports comprisepart of the machine in which the screw is to beused'or part of an assembly jig having its two halves'50 connected 'bycap screws in the manner shown in FIGURE'21.

To adjust and lock the nut sections accurately assembled, theassemblyman first applies a spanner wrench 53 (identical with spannerwrench 47 of FIGURES 18 and 19 of my earlier patent) to-theleft-hand nutsection A, FIGURE 21 and rotatesit forcibly against end surface 54 ofthe supporting" bearing for screw 1. Since screw 1 is then heldstationary it will be recognized that continued rotation of the nut tothe left applies loading to those balls 18 of the. ball circuit then incontact with screw groove 16. A predetermined load force W is'applied tothe outer'end of the spanner wrench and maintained as the next nut ringR is similarly rotated against the adjacent face of nut ring A with anidentical spanner wrench under the same applied loading W. If thelocking key receiving keyways 52 are in alignment a locking key 56 ispressed into place locking nut sections A and B against relativerotation. It sometimes happens that keyways 52 are not then inalignment. In these circumstances, the nut undergoing, adjustment canbecounter-rotated to permit insertion of a shim 55 of the requisitethickness to' align the keyways 52 as the same are rotated into abutmentunder the desired applied load W. V I

The assemblyman continuesto adjust each of the remaining nut sections Cand B in order following the same procedure described in connection withsections A and B until all have been locked in assembled position whilethe first nut section. remains rotated against the screwsupportingbearing. Once all nut sections have been properly andaccurately adjusted and locked together, the wrenches are: removed andthe unitary nut assembly of rigidly interlocked components is free torotate along the screw. So long as there is no applied external load, itwill be recognized that the rigidly'assembled nut unit cation of a loadsuch load will be equally and automatiwill have limited axial movementwith respect to the tributed load acting along diagonal lines arrangedat substantially the same angle withrespect to the screw axis. As thenut assembly and screw rotate relative to one cally distributed betweenall balls in contact with the screw; An example of a particularlyadvantageous application having need for these capabilities is the.landing gear'of an aircraft. In this application, as will beappreciated, it is of the greatest importance that the losses betweenrelatively rotating parts be held to a minimum and yet that maximumadvantage be'taken of the strength of the structural material. It istherefore important that the extreme stresses imposed on the landinggear as the aircraft touches down on the landing strip be instantly andequally distributed between all load balls and all parts in contacttherewith. i

Referring to FIGURES 3 to 12, another preferred embodiment of theinvention incorporating the features of the present invention will bedescribed. Referring first to FIGURE 23, there is shown a ball bearingscrew and nut mechanism in atypical operating environment having a screw10' journalledin ball bearings 11 and driven through suitable gearing byan electric motor 12'. Mounted on screw 10 is a preloaded ball bearingnut mechanism designated generally 13 constructed in accordance with thepresent invention and connected through pivoted arm714' to a device suchas an airplane landing gear, not shown, which it is desired to shiftlinearly. The construction is such that rotation of screw 10' by motor12' elfects linear movement of nut mechanism 13' and of the devicearranged to be driven through arms 14'.

Referring to FIGURE 24, nut mechanism 13' is shown ascomprising'aplurality of identical annular nuts or nut rings 16 mountedwithin a retaining sleeve 17 and held rigidly compressed against oneanother by adjustable end rings 18', the latter being threadedlyinserted into the sleeve ends. 'Any number of nut rings 16', from one toa large'number, may be employed, depending upon the design requirementsof the particular; screw and nut system. Each nut or nutring16' is,provided with an internal helical groove corresponding to the externalgroove on screw 10' and cooperating therewith to form the major or loadloop of a' race for a plurality of balls 20. Balls 20' extend along atleast one full turn or loop of the screw and nut grooves, theendportions of the'sin'gle turn load groove preferably being overlappedslightly as shown to assure uniform distribution of the applied loadthroughout the entire circumference of thescrew and of the nut rings.The overlapped ends of the load groove ballsare positioned opposite agenerally semi-cylindrical bore 21' formed ineach nut ring and extendingfrom face to face of the nut ring. Bore 21' serves to receive a ballreturn insert 22 (FIGURES 7 and 8) employed to transfer'the balls 20from one end of theload groove to the other end thereof and forming thesmall diameter ball return loop portion of the .ball circuit. Insert 22'may be secured in nut ring 16 by any suitable means 'such as by welding,

another, the balls in the independent ball circuits of each nut sectionrotate as they circulate along the load groove.

and through the ball return loops of each circuit.

Thus, it has been shown that the nut rings 14, and likewise nut rings"and 32, can be manipulated on the screw 1 to load'the balls 18uniformly to carry an applied load. 1 Y

However, owing to the initial precision assembly of the nut ringsrelative to one another and to the screwwith each load ball of each nutbeing placed under uniform preloads of a known value, the application ofan external load results in each ball assuming its own uniform share ofthe load instantly. The described capability and char acteristics of theembodiment shown in FIGURES 1 and V or by use, of a pin 23' in themanner shown in FIGURE 5. This insert may be formed from metal orplastic by use of die' casting, injection molding,powdered metal orother techniques.

According t-othe presentinvention, insert 22"is so constructed thatballs20 reverse direction two times in va smooth curve andform a smalldiameter return loopmerging with the 'ends of the large diameter loadgroove loop thereby providing acomplete ball racehaving a figure eightconfiguration as is best illustrated in FIG- URE 12. More specifically,insert 22' is constructed with a generally semi-cylindrical body 25corresponding in a size to bore 21 and includes depending ears 26 and27" 2 are of very censiderable importance becausethey provide theadvantages of constantly preloaded nut assemblies described in myaforementioned patent without need formed one at each end portion ofbody 25" and on the opposite sides thereof. Theears 26 and 27' dependinto screw groove 16 andiscrew 10 and serve as guides for the smooth andeflicient transfer. of balls 201b tw een the large diameter load groovesand the relatively sma l. diameter ball return loop;

The loop-shaped passage through insert 22' comprises a groove 28'extending generally diagonally or obliquely to the longitudinal axis ofinsert body 25' as viewed in FIGURES 9 and 11, and terminates at theends of ears 26' and 27'. Groove 28' opens outwardly along the outerside of the semi-cylindrical wall of insert body 25' so that balls 29'actually roll along the corresponding semicylindrical wall of bore 21'in nut ring 16', but is separate from the screw thread crest by atransverse bridge 29 (FIGURE 6), this bridge serving to complete theball return loop and to maintain the balls out of contact with the crestof the screw thread. As is best illustrated in FIGURES 7 and 10, ears 26and 27' are formed, respectively, with faces 31' and 32 which are socurved as to have the same radius and center as the wall of nut bore21', so that these faces 31' and 32' are in perfect cylindrical orcurvilinear continuity with the bore wall. In order to provide for thiscontinuity the ears 26 and 27' are recessed back into the nut body, andprotrude outwardly in opposite directions from insert body 25, as isbest illustrated in FIGURE 9.

In the operation of the described illustrative embodiment of theinvention shown in FIGURES 3 to 12, let it be assumed that thecomponents of the ball bearing nut and screw mechanism 13' have beenassembled to place these rings under compression axially of themechanism with all of balls 20' actually in the large diameter loadgroove of each of the independent ball circuits under predetermined,uniformly distributed preload stress independently of external loadconditions. Assuming now that screw is rotated counterclockwise relativeto nut rings 16 as viewed in FIGURES 5 and 7, the balls in the largediameter load groove formed by the mating grooves of the screw and thenut rings will roll counterclockwise relative to nut rings 16' until theballs engage faces 31' of ears 26'. The balls then roll upwardly alongfaces 31' in a smooth curve and onto the wall of bore or channel 21,these surfaces being in true curvilinear continuity due to the fact thatface 31' lies on the interior surface of the same hypothetical cylinder,extending longitudinally of the screws, as the bore wall. Balls 20 thenloop backwardly and outwardly through groove 28' between the overlappedends of the large diameter single turn load groove loop or convolution.The balls are thus guided by the wall of channel 21', by the side wallsof the insert body 25', and by the upper rounded wall of bridge 2? untilthey roll onto face 32' of car 27' and thus back into the load groove.

It is to be noted that the balls in rolling upwardly on face 31' andinto groove 28 reverse direction and are guided back over a screw threadcrest in the small diameter ball return loop portion of the figure eightrace, after which the balls again reverse direction and roll downwardlyonto face 32' of car 27' and back into the single turn load grooveconvolution between the screw and the nut ring. There is absolutely nobreak in the continuity of the walls over which the balls 20 are guided,and there are no sharp points or friction generators in the entirefigure eight race. The balls thus move through the entire race inextremely frictionless manner so that the efficiency of the screw andnut mechanism is greatly increased as compared to former structures inwhich the balls do not roll in a figure eight but instead merely make agenerally right angle turn over the screw thread crest. In circulatingthrough the described closed loop circuits, it is pointed out that allballs within the main load groove of at least one full convolution ofthe screw are always maintained preloaded and elastically deformed bythe preload forces with the result that each nut ring carries a fullshare of the applied load which share is distributed uniformly betweenall balls in the load groove.

While the particular preloaded ball bearing screw and nut mechanismherein shown and disclosed in detail is fully capable of attaining theobjects and providing the advantages hereinbefore stated, it is to beunderstood that it is merely illustrative of the presently preferredembodiments of the invention and that no limitations are intended to thedetails of construction or design herein shown other than as defined inthe appended claims.

I claim:

1. A ball bearing nut and screw mechanism comprising a screw having ahelical ball seating groove extending therealong, a plurality of similarnut rings encircling said screw and having inwardly opening helicalgrooves substantially identical to said screw groove, each nut ringhaving a single full convolution load groove opening at its ends intoball return passage means formed in the body of the nut ring, said nutrings each being held assembled to said screw by independent closedcircuits of recirculating balls, each of said circuits having a figureeight configuration, recess means extending crosswise of said rings andpositioned to be in aligned registry with one another as said rings areheld rotated against a fixed abutment adjacent said screw by a forcesufiicient to load the balls in contact with the screw by predeterminedload values, and rigid close fitting key means extending through saidaligned recesses to lock said nut rings precisely in the definedpositions thereof to the end that an externally applied load will bedistributed to all balls seated in said load convolutions.

2. A ball bearing nut and screw mechanism comprising a screw having ahelical groove, a nut assembly encircling said screw and held assembledthereto by a plurality of independent continuous circuits ofrecirculating balls held captive between the helical groove of saidscrew and an associated complementary helical groove means formed alongthe inner side wall of said nut assembly, the latter groove meansincluding ball return means for passing the balls of each ball circuitbetween the opposite ends of the portion of the circuit formed by thehelical groove of said screw, said nut assembly including a plurality ofnut sec tions rotated relative to one another axially of said screw toposition the independent continuous circuit of recirculating balls insuch manner as to load balls of each ball circuit against one side wallof the screw groove and along a path passing diagonally through theballs and substantially identically inclined to the longitudinal axis ofthe screw when the assembly is under load, and means for locking saidnut sections rigidly locked against relative counter-rotation therebyproviding a nut assembly having limited freedom of movement axially ofsaid screw when there is no applied external load as well as one whereinthe balls of the several independent ball circuits in contact with thehelical groove of said screw are automatically placed undersubstantially equal loads simultaneously as an external load is appliedto said mechanism.

3. A ball bearing nut and screw mechanism as defined in claim 2characterized in that said means for locking said nut rings rigidlyagainst relative counter-rotation comprises rigid means seated in snuglyfitting keyway recesses extending crosswise of said nut rings andaligned with one another when the nut rings are precisely rotated todistribute an externally applied load uniformly to the balls associatedwith each of said nut rings.

4. A ball bearing nut and screw mechanism as defined in claim 3characterized in the provision of shim means between adjacent nut rings,the thickness of the shim means employed being selected to permit andassure a desired uniformly distributed load on the balls in contact withsaid screw when keyway recesses of adjacent nut rings are in alignmentand positioned to seat a common rigid means for locking said nut ringsagainst relative rotary movement.

5. A ball bearing nut and screw mechanism wherein all balls in contactwith the screw are adapted to share an externally applied loadsubstantially uniformly and at the same time, said mechanism comprisinga screw having a helical groove extending through a rigid unitary nutassembly composed of a plurality of like nut sections arrangedvside-by-side'along said-screw and locked together underpredeterminedaxially acting load forces, each of said nut sections having i-ts ownindependent circuit of recirculating balls including a ball return 'loopportion external to the screw groove and a load groove portion whereinmost of the balls of a givencircuit are in contact with the screwgroove, means for locking the nut sections of saidv assembly againstrelative rotation with the load groove portions oftheir respectivecircuits.

when no load is being applied to said ball bearing nut and screwmechanism. 7

' 'ReferencesCited by the Examiner. UNITED STATES PATENTS 2,659,24111/53 Holman 74 -424.8

2,749,812 6/56' Wetzel 74441 7/56 [Hogan et a1. 74-459 FOREIGN PATENTS570,789 1/24 I France. 725,181 9/42 Germany. 7 583,532 12/46 GreatBritain.

BROUGHTON G1 DURHAM, Primary Examiner.

15 FRANK BRONAUGH, DON A. WAITE, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No;3,198,029 August 3, 1965 Harry Orner It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 6, line 18, after "rotated" insert in the same direction Signedand sealed this 19th day of April 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A BALL BEARING NUT AND SCREW MECHANISM COMPRISING A SCREW HAVING A HELICAL BALL SEATING GROOVE EXTENDING THEREALONG, A PLURALITY OF SIMILAR NUT RINGS ENCIRCLING SAID SCREW AND HAVING INWARDLY OPENING HELICAL GROOVES SUBSTANTIALLY IDENTICAL TO SAID SCREW GROOVE, EACH NUT RING HAVING A SINGLE FULL CONVOLUTION LOAD GROOVE OPENING AT ITS ENDS INTO BALL RETURN PASSAGE MEANS FORMED IN THE BODY OF THE NUT RING, SAID NUT RINGS EACH BEING HELD ASSEMBLED TO SAID SCREW BY INDEPENDENT CLOSED CIRCUITS OF RECIRCULATING BALLS, EACH OF SAID CIRCUITS HAVING A FIGURE EIGHT CONFIGURATION, RECESS MEANS EXTENDING CROSSWISE OF 